getsockopt, setsockopt - get and set options on sockets
#include <sys/types.h> /* See NOTES */
int getsockopt(int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
int setsockopt(int sockfd, int level, int optname,
const void *optval, socklen_t optlen);
() and setsockopt
() manipulate options for the socket
referred to by the file descriptor sockfd
. Options may exist at
multiple protocol levels; they are always present at the uppermost socket
When manipulating socket options, the level at which the option resides and the
name of the option must be specified. To manipulate options at the sockets API
is specified as SOL_SOCKET
. To manipulate options
at any other level the protocol number of the appropriate protocol controlling
the option is supplied. For example, to indicate that an option is to be
interpreted by the TCP
should be set to the
protocol number of TCP
; see getprotoent(3)
The arguments optval
are used to access option values
(). For getsockopt
() they identify a buffer in
which the value for the requested option(s) are to be returned. For
is a value-result argument, initially
containing the size of the buffer pointed to by optval
, and modified on
return to indicate the actual size of the value returned. If no option value
is to be supplied or returned, optval
may be NULL.
and any specified options are passed uninterpreted to the
appropriate protocol module for interpretation. The include file
contains definitions for socket level options,
described below. Options at other protocol levels vary in format and name;
consult the appropriate entries in section 4 of the manual.
Most socket-level options utilize an int
argument for optval
(), the argument should be nonzero to enable a boolean
option, or zero if the option is to be disabled.
For a description of the available socket options see socket(7)
appropriate protocol man pages.
On success, zero is returned for the standard options. On error, -1 is returned,
is set appropriately.
Netfilter allows the programmer to define custom socket options with associated
handlers; for such options, the return value on success is the value returned
by the handler.
- The argument sockfd is not a valid file descriptor.
- The address pointed to by optval is not in a valid part of the
process address space. For getsockopt(), this error may also be
returned if optlen is not in a valid part of the process address
- optlen invalid in setsockopt(). In some cases this error can
also occur for an invalid value in optval (e.g., for the
IP_ADD_MEMBERSHIP option described in ip(7)).
- The option is unknown at the level indicated.
- The file descriptor sockfd does not refer to a socket.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first appeared in
POSIX.1 does not require the inclusion of <sys/types.h>
, and this
header file is not required on Linux. However, some historical (BSD)
implementations required this header file, and portable applications are
probably wise to include it.
For background on the socklen_t
type, see accept(2)
Several of the socket options should be handled at lower levels of the system.
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